1. Field of the Invention
The present invention relates to a motor control apparatus, in particular to a motor control apparatus having a function of detecting miswiring of motor signal lines.
2. Description of the Related Art
In order to drive a motor, power lines to the motor and signal lines to detectors need to be connected to a motor control apparatus. Since connection of these power lines and signal lines is manually performed, miswiring could happen frequently.
As examples of miswiring of power lines, wrong phase procedures, open phases, short-circuits and the like are listed. As a means for mechanically determining whether or not power lines are miswired, there have been known methods such as a method of detecting excess or deficiency of electric current under application of voltage (e.g., Japanese Unexamined Patent Publication (Kokai) No. H09-16233) and a method of performing a comparison between the current value and motor torque (e.g., Japanese Unexamined Patent Publication (Kokai) No. H07-20190).
As an example of miswiring of signal lines, there is a case where, when there exist multiple pairs of a detector and a motor control apparatus, the motor control apparatuses are connected to wrong detectors, by mistakenly selecting wrong combinations. As a means for mechanically determining whether or not the signal lines are miswired, there have been known methods such as a method in which the detector type designated by a parameter and the actually connected detector are compared so as to detect whether or not the designated detector is correctly connected (e.g., Japanese Unexamined Patent Publication (Kokai) No. 2004-103031, which will be referred to hereinbelow as “Patent Document 3”).
Other than the above detecting methods, methods of determining whether or not the power lines and signal lines are connected correctly by actually driving the motor have been generally used.
Use of the prior art makes it possible to detect miswiring of power lines even for motors having multiple windings. However, for detection of miswiring of signal lines, when the detection method of Patent Document 3 is used, detection of miswiring is difficult when the same type of detector is used in multiple motors.
Further, in a mechanical configuration in which a single axis is driven by multiple motors, if the phases of the individual motors coincide with one another, no faults are detected from the detectors so that the axis can be driven despite miswired conditions, though the motors may be lowered in power factor and become unstable from a control viewpoint.
Next, miswiring in conventional motor control apparatuses will be described. FIG. 1 is a block diagram showing a miswired condition of signal lines with multiple motors and motor control apparatuses in the prior art. One motor is driven by one corresponding motor control apparatus. In a machine in which multiple axes are operated, there are multiple pairs each composed of a motor and a corresponding motor control apparatus. FIG. 1 shows an example where two pairs of a motor and a motor control apparatus are provided. A motor control apparatus A (1001A) controls a motor A (10A) via a power line (not shown) while a motor control apparatus B (1001B) controls a motor B (10B) via a power line (not shown).
As to signal lines from detectors, the motor B (10B) is connected with the motor control apparatus A (1001A) via a wiring line 30A while the motor A (10A) is connected with motor control apparatus B (100B) via a wiring line 30B. In this way, when multiple pairs of a motor and a motor control apparatus are provided, it often happens that signal lines from detectors are miswired with wrong motor control apparatuses despite that the power lines are connected correctly. If the motors are driven in the miswired condition as above, the phases of the rotors cannot be fed back correctly, so that there is a risk that the motors are controlled and driven with excessive currents.
In the method shown in Patent Document 3, the model of the detector to be used for the motor control apparatus is entered as a parameter, and when the connected detector does not correspond to the entered model, miswiring is detected.
However, this method has the problem that miswiring cannot be detected when multiple motors use the same type of detectors because it is impossible to distinguish one detector from another.
Further, miswiring may occur when one single axis is driven by multiple motors (tandem drive). FIG. 2 is a block diagram showing miswiring of signal lines in tandem driving mode in the prior art. FIG. 2 shows an example where two pairs of a motor and a motor control apparatus are provided to drive a single axis 100. Connections of power lines of motor control apparatuses A (1002A) and B (1002B) with respective motors A (10A) and B (10B) by power lines (not shown) and connections of signal lines from the detectors are the same as those in the example shown in FIG. 1.
In the tandem drive, since the rotor phases of the multiple motors rotate simultaneously, the motors apparently seem to drive normally if the rotor phases of the multiple motors coincide with each other by chance. However, once the rotator phases become different from each other for some unspecified reason, the motors rotate in full torque, conceivably having serious influence such as causing damage to the machine itself or the work.